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"You wanna know why this room was locked up? This is what I found in here. A painted record of every horrible thing my family's ever done: lying, cheating. And then there's me: I lied to you just because I'm too scared to talk back to my stupid parents. You were right about me, I am just another link in the world's worst chain."
- Pacifica Northwest
She comes from a rich family, who it was believed founded Gravity Falls, until Dipper and Mable managed to prove her ancestor, Nathaniel Northwest didn't found Gravity Falls and was instead an idiot who shoveled horse dung. Who was claimed was the founder, to cover a government conspiracy to remove the true founder from history.
In "The Golf War" Pacifica embarrasses Mabel and challenges her to a mini golf tournament. It is shown in the episode that she does not live quite a normal life. She receives a lot of pressure from her parents to be the best at everything, does not know how to react to common behaviour (like eating in the car or sharing), and lives in a mansion with fountains and peacocks. She also does not receive much support from her parents as they often put important parties and business matters before her.
In "Northwest Mansion Mystery" Pacifica goes to Dipper for help with dealing with The Lumberjack Ghost who has began haunting Northwest Manor, on the eve of an industrious party they have planned. Dipper reluctantly agrees, however while Dipper and Pacifica hang out and save each others lives, they begin to bond. After capturing the ghost, Dipper I left rethinking his opinion of her. Until the ghost tells him why he was haunting their mansion and that the Northwest's knew how to break the curse, but rather have Dipper do their dirty work than damage their pride.
Furious he returns to call them out. Pacifica is actually happy to see his return, but Dipper's speech about the Northwest's cuts her down, with him accusing her of being just as bad as her family. Pacifica then begins to have a breakdown, having discovered the truth about her families legacy in a hidden room, she and Dipper are found while chasing the ghost. Its revealed in this episode that as opposed to simply being neglectful, her parents are outright abusive towards her. Her father, Preston Northwest having actually conditioned her to respond to a bell like a dog.
When the ghost escapes and begins terrorizing party, Dipper returns and realizing Pacifica could break the curse, goes to find her. She's still in the room, now having broken down and not caring she will probably die, deciding he was right and she is just as bad her horrible family legacy. Dipper manages to snap her out of it, encouraging her that she can break the trend. But by this point the ghost has already turned all the guests to wood and plans to burn Northwest Mansion down, killing everyone.
Dipper tries to confront it, but the ghost overpowers him and he to is turned to wood. Finally stepping up, Pacifica tries to open the main gates letting people into enjoy the party, which will break the curse. However her father having hid in the Panic room, orders her not to, unwilling to let the common people in even in these circumstances. Finally standing up to her abusive father, Pacifica opens the gates and breaks the curse, saving everyone's life and as a final act of rebellion stands on her parents favorite silver patterned carpet with muddy shoes.